Measurements of total petroleum hydrocarbons (TPH) in soils are often required to assess environmental remedial endpoints and satisfy regulatory requirements. Soil TPH concentrations can be obtained in analytical laboratories, typically using gas chromatography (GC) such as GC with a flame ionization detector (GC-FID). However, lengthy turnaround times of weeks to months can cause significant delays in field operations, e.g., during soil treatment processes, when such laboratory techniques are used. A method that can quickly generate TPH concentration in soil of sufficient quality to make real-time field decisions would be useful to decrease the time requirements for soil remediation, reduce the number of samples that have to be analyzed by a laboratory, allow for quick follow-up sampling during site assessment and/or reduce uncertainty due to increased sampling density, ultimately reducing the overall project cost. Field test kits for soil TPH analyses are commercially available, but typically require a solvent extraction step, which makes them time consuming and complicated to use in the field. Near- and mid-DRIFT (Diffuse Reflectance Infrared Fourier Transform) using portable spectrometers have also been shown to give promising results for estimating TPH concentration in soils. Reflectance IR spectra can be acquired easily and rapidly because of the high sensitivity of alkyl-CH3 vibrational group. However, these methods require a time-consuming step to dry each sample.
In attenuated total reflectance (ATR) Fourier transform infrared spectroscopy, also referred to interchangeably as FTIR-ATR and ATR-FTIR, infrared light is introduced into a prism at an angle exceeding a critical angle for internal reflection. An evanescent wave is produced at the surface on which the sample is supported, extending into the sample. The evanescent wave is distorted by the sample resulting in a spectrum. The spectrum is measured and subjected to a Fourier transform.
Despite advances in the field, there still exists a need for an alternative method for estimating total petroleum hydrocarbons concentration in contaminated soils quickly and simply, without the need for time consuming sample preparation.